The present invention relates to apparatus and methods for removing and installing a selected nozzle segment relative to a nozzle retention ring of a gas turbine and particularly relates to axially oriented anti-rotation pins for preventing circumferential movement of the nozzle segments and enabling removal and insertion of the anti-rotation pins in an axial direction to facilitate removal and installation of a selected nozzle segment without removal of the casing.
In gas turbines, the nozzle stages are typically formed by an annular array of nozzle segments spaced circumferentially one from the other about the axis of the turbine. For example, in the first stage of the turbine, the nozzle segments, each including outer and inner bands with one or more nozzle vanes extending therebetween, are secured to annular outer and inner retention rings, respectively. In prior gas turbines, anti-rotation pins typically extend radially between the outer retention ring and an outwardly projecting flange on the outer band of each segment. These radially oriented prior anti-rotation pins encounter space limitations which prevent removal of certain of the pins when performing turbine maintenance in situ. For example, at the horizontal joint, the case is very close to the retention ring and the anti-rotation pin cannot be removed, leaving the nozzle segments essentially non-removable. As a consequence, maintenance and testing operations have been found to be laborious and costly. Therefore, there is a need to generally improve the capability for removing and installing nozzle segments to facilitate maintenance and testing operations.